1. Field of the Invention
This invention relates to a plastic cap for containers and more particularly, to a plastic cap with a guarantee ring.
2. Description of the Prior Art
Numerous plastic caps are known (DE G 87 09 690.0; U.S. Pat. No. 4,666,053) which are used to close any type of container. The caps have a guarantee ring which serves to indicate that the closed container has not been previously opened. During a first attempt at opening the container, the guarantee ring will snap open, so that a consumer can readily note that the container is no longer closed in the original way.
In the case of the caps produced in a forming process (DE G 87 09 690.0 U1), it was found that the zones of a smaller wall thickness which tear during the bursting-open of the guarantee ring and which are also called vertical incisions, in the end do not have any defined wall thickness so that the tearing-open behavior of the cap cannot be reliably predetermined. In the case of caps which have tear zones defined by a cutting operation (U.S. Pat. No. 4,666,053), it is in many cases not possible to introduce the bursting forces occurring during the first opening into defined areas of the guarantee ring in order to ensure a reliable tearing. In both cases, it is therefore possible that a first opening of the container may not be indicated to the consumer.
Finally, metal caps are known (see U.S. Pat. No. 4,217,989) which are subjected to a forming as well as a cutting process during a single manufacturing operation. However, processes of this type cannot be applied to plastic caps of the type addressed here because the plastic forming process cannot be combined with a cutting operation.
During the production of the caps and the associated containers, naturally size deviations occur. It may happen that a cap with a maximum inside diameter that lies within the tolerance range is combined with a container, the outside diameter of which does, it is true, lie within the tolerance range, but has the smallest outside diameter that is still possible. In such a case it is possible that during the first opening of the container, the forces exerted on the guarantee ring or guarantee area are not sufficient to make it snap open, so that it slides undamaged over the outside wall or the mouth part of the container when the cap is opened for the first time. This is, in particular, due to the fact that the so-called vertical incisions, by which the guarantee area is split into at least two segments, have too great a production-related strength.